Background: We assessed the scientific basis and practical implications of recommendations made since the late 1990s to offer rabies postexposure prophylaxis (RPEP) for occult bat encounters, including recommendations to offer RPEP to persons with bedroom exposure to a bat while sleeping without evidence of direct physical contact.
Methods: The number needed to treat after bedroom exposure to a bat was calculated as the percentage of population exposed multiplied by the inverse of crude rabies incidence. Bedroom exposure was estimated in a population survey of 14,453 households. Incidence was based on reported human cases in Canada and the United States, 1990-2007.
Results: In the population surveyed, bedroom bat exposure while sleeping and without known physical contact occurred at an annual rate of 0.099%. We estimate that <5% of eligible persons with bedroom exposure receive RPEP as recommended. The incidence of human rabies due to bedroom bat exposure without recognized contact was 1 case per 2.7 billion person-years. The number needed to treat to prevent a single case of human rabies in that context ranges from 314,000 to 2.7 million persons. A total of 293-2500 health care professionals working full-time for a full year would be required to prevent a single human case of bat rabies due to bedroom exposure without recognized contact. Amounts of Can $228 million to Can $2.0 billion are additionally required for associated material costs.
Conclusions: Human rabies acquired through bedroom exposure to a bat while sleeping and without recognized contact is rare. Conversely, such exposures are not uncommon in the population, and the resources required for associated RPEP are orders of magnitude higher than those required for most interventions that are considered to be reasonable. Current RPEP recommendations related to occult bat contact should be reconsidered.